Radiation-activated tetravalent platinum complex and use thereof

ABSTRACT

The present disclosure provides a complex of general formula (I), wherein M is tetravalent platinum; L is independently a neutral ligand or an anionic ligand when appearing each time; x is an integer of 1-5; P is a precursor ligand, the precursor ligand being a ligand of a tetravalent platinum ion which can be released from the complex after irradiation and converted into a functional molecule D to achieve functions such as medicine, fluorescence detection, or a functional material. 
       L x -M-P  (I)

FIELD OF THE INVENTION

The present disclosure relates to the field of radiation chemistry, inparticular to a radiation-activated tetravalent platinum complex and ause thereof.

BACKGROUND OF THE INVENTION

Cancer is the second leading killer threatening people's health. Atpresent, chemotherapy is the main clinical treatment for cancer.Platinum-based drugs have high-efficiency and broad-spectrum anti-canceractivity; thereby having become clinically important first-linechemotherapy drugs, and being widely used in the treatment of commonmalignant tumors such as lung cancer, bladder cancer, ovarian cancer,cervical cancer, esophageal cancer, gastric cancer, colorectal cancer,and head and neck tumors. The first generation of platinum-basedanticancer drugs is represented by cisplatin; the second generation ofplatinum-based anticancer drugs is represented by carboplatin,nedaplatin, and cycloplatin; and the third generation of platinum-basedanticancer drugs is represented by oxaliplatin and lobaplatin. Theseplatinum-based anticancer drugs are mainly complexes of divalentplatinum. Tetravalent platinum compounds themselves have low killingability to cancer cells, and can exert anticancer activity by beingreduced and releasing divalent platinum under physiological conditions.Tetravalent platinum compounds not only retain the broad-spectrum andhigh-efficiency anticancer advantages of traditional divalent platinumdrugs, but also bring other unique advantages because of thecoordination structure of tetravalent platinum different from divalentplatinum. Tetravalent platinum has a d²sp³ hexa-coordination structure,and has stability stronger than that of divalent platinum thereby havinghigher blood stability. The tetravalent platinum complex possesses twoadditional ligands in the axial direction, which provides more optionsfor the design of platinum-based drugs. Tetravalent platinum can notonly be subjected to structural modification on the horizontal ligandbut also on the axial ligand, such as introducing functional groups forlipid-water adjusting, enzyme targeting. DNA targeting, or serum albumintargeting into the axial ligand.

At present, many studies have been carried out on platinum-basedcompounds, and the defects of platinum-based drugs, such as strong toxicside effects, low absorption, poor targeting, and serious drugresistance, have been discovered. Therefore, there is still a need todevelop a novel platinum-based compound. However, at present, there isno report on the introduction of a radiation-responsive molecule into aligand of a tetravalent platinum-based compound.

In addition, there is no report on the use of radiation to releasefunctional molecules from ligands of tetravalent platinum-basedcompounds to achieve functions such as medicine, fluorescence detectionand functional materials.

SUMMARY OF THE INVENTION

One aspect of the present disclosure provides a metal complex of generalformula (I),

L_(x)-M-P  (I)

wherein M is tetravalent platinum; L is independently for eachoccurrence a neutral ligand or an anionic ligand: x is an integer from 1to 5; and P is a precursor ligand, the precursor ligand being a ligandof the tetravalent platinum ion which can be released from the complexafter irradiation and converted into a functional molecule D.

In some embodiments, the functional molecule D is selected from drugmolecules, fluorescent molecules, and functional material molecules. Insome preferred embodiments, the functional molecule D is an anticancerdrug molecule. In some more preferred embodiments, the functionalmolecule D is an anticancer drug molecule, and at least one L has agroup targeting tumor cells. For example, the L having a group targetingtumor cells includes a sugar transporter targeting group, a glutaminereceptor targeting group, a phosphate receptor targeting group, anepidermal growth factor receptor targeting group, an integrin targetinggroup, an energy metabolism enzyme targeting group, a chondriosometargeting group, a serum albumin targeting group, an inflammatory factortargeting group, a DNA targeting group, a histone deacetylase (HDAC)targeting group, a P53 gene activator group, a tubulin inhibitor group,a cyclin-dependent kinase inhibitor group, or an indoleamine2,3-dioxygenase inhibitor group.

In some embodiments, the functional molecule D is selected frommonomethyl auristatin E, monomethyl auristatin F, ibrutinib, acatinib,zanubrutinib, doxorubicin, mitomycin-C, mitomycin-A, daunorubicin,aminopterin, actinomycin, bleomycin, 9-aminocamptothecin,N8-acetylspermidine, 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine,yunnanmycin, gemcitabine, cytarabine, dolastatin, dacarbazine,5-fluorouracil, paclitaxel, docetaxel, gemcitabine, cytarabine; and6-mercaptopurine. In some preferred embodiments, the functional moleculeD is monomethyl auristatin E, monomethyl auristatin F, or5-fluorouracil.

In some embodiments, at least one ligand L is selected front NH₃,ethylenediamine, oxalate, malonate, 1,2-diaminocyclohexane,1,2-diaminobenzene, 2-aminopropane, aminocyclohexane,cyclobutane-1,1-dicarboxylate, glycolate, lactate, aminocyclohexane,2-isopropyl-4,5-bis(aminomethyl)-1,3-dioxolane,5-(triphenylphosphonio)valerate, succinate,6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoate, porphyrin, acetate,and propionate.

In some embodiments, one ligand L is an axial ligand capable of beingreleased from the complex after irradiation and converted into afunctional molecule which may be the same as or different from thefunctional molecule D.

In some embodiments. P is an axial ligand.

In some embodiments, P is ⁻O—C(═O)—X—Y, wherein

-   -   X is —NH—, —NR—, —O—, or —S—. R is an optionally substituted        C₁₋₁₀ alkyl, and HXY constitutes the functional molecule D; or    -   X is —CH₂—, —CRH—, or —CR₂—, wherein R is independently for each        occurrence an optionally substituted C₁₋₁₀ alkyl, or two R        groups are taken together with the carbon atom to which they are        attached to form a 5-membered ring or a 6-membered ring, and        HOOCXY constitutes the functional molecule D.

Another aspect of the present disclosure also provides a use of theabove metal complex of the general formula (I) in the fields ofmedicine, detection or functional materials, etc., wherein the metalcomplex of general formula (I) releases a functional molecule from aligand after irradiation to realize functions such as medicine,fluorescence detection or functional materials.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to illustrate the technical solutions of the examples of thepresent disclosure more clearly, the drawings of the examples will bebriefly introduced below. Apparently, the drawings in the followingdescription only relate to some examples of the present disclosure,rather than limiting the present disclosure.

FIG. 1 shows the ligand release percentage of 10 μM tetravalent platinumcomplexes 19-31 after 60 Gy of X-ray irradiation.

FIG. 2 shows the reaction schematic diagram, the fluorescence changediagram, and the UPLC change diagram for screening tetravalent platinumcompounds 32, 33, and 34 that are stable in vivo.

FIG. 3 shows the result of in vivo activation test of tetravalentplatinum compound 35 with oxaliplatin as a parent.

FIG. 4 shows the result of activation test of a radiation-responsiveantibody-drug conjugate with platinum as a linker.

FIG. 5 shows the broad-spectrum and high-efficiency release ofFDA-approved Pt(II) drugs from Pt(IV) complexes driven by radiation.

FIG. 6 shows the construction and characterization of ADCs whose drugrelease can be driven by radiotherapy.

FIG. 7 shows the pharmacokinetic properties of OxaliPt(IV)-ADC.

DETAILED DESCRIPTION OF THE INVENTION

In order to make the purpose, technical solutions and advantages of theexamples of the present disclosure clearer, the technical solutions ofthe examples of the present disclosure will be clearly and completelydescribed below in conjunction with the drawings of the examples of thepresent disclosure. Apparently, the described examples are a part of theexamples of the present disclosure, not all of the examples of thepresent disclosure. Based on the described examples of the presentdisclosure, all other examples obtained by those of ordinary skill inthe art without creative effort shall fall within the protection scopeof the present invention.

The present disclosure may be embodied in other specific forms withoutdeparting from essential attributes of the present disclosure. It shouldbe understood that any and all embodiments of the present disclosure canbe combined with technical features in another embodiment or otherembodiments to obtain additional embodiments under the premise of noconflict. The additional embodiments resulting from such combinationsare included by the present disclosure.

All publications and patents mentioned in this disclosure are herebyincorporated by reference into this disclosure in their entirety. To theextent that usage or terminology used in any publications and patentsincorporated by reference conflicts with usage or terminology used inthe present disclosure, the usage and terminology in the presentdisclosure shall control.

The section headings used herein are for the purpose of organizing thearticle only and should not be construed as limitations on the subjectmatter described.

Unless defined otherwise, all technical and scientific terms used hereinhave their ordinary meanings in the art to which the claimed subjectmatter belongs. In the event that more than one definition exists for aterm, the definition herein controls.

Unless otherwise stated, when any type of range is disclosed or claimed(e.g., number of ligands), it is intended that each possible value thatthe range could reasonably encompass is individually disclosed orclaimed, including any sub-ranges encompassed therein. For example, thenumerical range of ligand L herein, such as 1-5, indicates an integerwithin the range, wherein 1-5 should be understood to include 1, 2, 3,4, 5, and also include the ranges of 1-4 and 1-3.

The description of the present disclosure should be construed inaccordance with the laws and principles of chemical bonding. In somecases it may be possible to remove a hydrogen atom in order toaccommodate a substituent at a given position.

The words “comprising”, “including” or “containing” and similar wordsused in the present disclosure mean that an element appearing before thewords covers elements listed after the words and equivalents thereof,and does not exclude any unrecited element. The term “comprising” or“including (containing)” used herein can be open, semi-closed andclosed. In other words, the term also includes “consisting essentiallyof” or “consisting of”.

As used herein, the terms “moiety”, “structural moiety”, “chemicalmoiety”, “group”, and “chemical group” refer to a specific segment orfunctional group in a molecule. A chemical moiety is generallyconsidered to be a chemical entity embedded in or attached to amolecule.

It should be understood that a singular form (e.g., “a”) as used in thisdisclosure may include plural referents unless otherwise specified.

Unless otherwise indicated, this disclosure employs standardnomenclature and standard laboratory procedures and techniques ofanalytical chemistry, synthetic organic chemistry, and coordinationchemistry. Unless otherwise stated, the present disclosure adoptstraditional methods of mass spectrometry and elemental analysis, and thesteps and conditions can refer to the conventional operation steps andconditions in the art.

The reagents and starting materials used in the present disclosure arecommercially available or can be prepared by conventional chemicalsynthesis methods.

The term “optional” used herein to describe a situation means that thesituation may or may not occur. For example, being optionally fused to aring means that it is fused to or not fused to a ring. For example, theterm “optionally substituted” as used herein refers to beingunsubstituted or having at least one non-hydrogen substituent that doesnot destroy the desired property possessed by the unsubstituted analog.

In the present disclosure, unless otherwise specified, the number of“substitution” can be one or more. When the number of “substitution” ismore than one, it can be 2, 3 or 4. Moreover, when the number of the“substitution” is more than one, the “substitution” may be the same ordifferent.

In the present disclosure, the position of “substitution” can bearbitrary unless otherwise specified.

The term “axial ligands” as used herein refers to the two axial ligandsin the d²sp³ hexa-coordinated structure of tetravalent platinum, whichare released from a complex after the complex is reduced by irradiation.

The term “lateral ligands” as used herein refers to the four lateralligands in the d²sp³ hexa-coordinated structure of tetravalent platinum,which can still be coordinated with a divalent platinum ion or can bereleased from a complex after the complex is reduced by irradiation.

As used herein, the term “neutral ligand” or “anionic ligand” refers toa ligand capable of being coordinated with platinum, wherein the ligandis uncharged or negatively charged as a whole, but may locally have acation such as triphenylphosphonium or ammonium.

As used herein, the term “C₁-C₁₀ to alkyl” refers to a straight orbranched alkane chain containing 1 to 10 carbon atoms. For example,representative examples of C₁-C₆ alkyl include, but are not limited to,methyl (C₁), ethyl (C₂), n-propyl (C₃), isopropyl (C₃), n-butyl (C₄),tert-butyl (C₄), sec-butyl (C₄), isobutyl (C₄), n-pentyl (C₅), 3-pentyl(C₅), neopentyl (C₅), 3-methyl-2-butanyl (C₅), tert-amyl (C₅), andn-hexyl (C₆), etc. The term “lower alkyl” refers to straight or branchedchain alkyl having 1 to 4 carbon atoms. “Substituted alkyl” refers to analkyl group substituted with one or more substituents, preferably 1 to 4substituents, at any available point of attachment. The term “haloalkyl”refers to an alkyl group having one or more halogen substituents,including but is not limited to groups such as —CH₂Br, —CH₂I, —CH₂Cl,—CH₂F, —CHF₂, —CF₃, and the like.

The term “alkylene” as used herein refers to a divalent hydrocarbongroup as described above for “alkyl” but having two points ofattachment. For example, methylene is a —CH₂— group, and ethylene is a—CH₂—CH₂— group.

The terms “alkoxy” and “alkylthio” as used herein refer to an alkylgroup as described above linked via an oxygen bond (—O—) or a sulfurbond (—S—), respectively. The terms “substituted alkoxy” and“substituted alkylthio” refer to a substituted alkyl group linked via anoxygen or sulfur bond, respectively. “Lower alkoxy” is the group OR,wherein R is lower alkyl (alkyl containing 1 to 4 carbon atoms).

The term “halogen” as used herein refers to fluorine, chlorine, iodineor bromine.

The radiation sources of the present disclosure may be alpha, beta,gamma rays produced by the decay of radionuclides. X-rays, gamma rays,energetic electrons, protons, heavy ions produced by external radiationsources, alpha particles produced by boron neutron capture therapy(BNCT), and other possible external or internal sources of radiation arealso applicable to the present disclosure.

The high-energy rays used in radiotherapy have high spatial and temporalresolution, and high tissue penetration ability, and at the same timeare highly clinically relevant. Using high-energy rays in radiotherapyto activate precursor molecules and cane out chemical reactions in vivohas both basic research value and clinical application value.

The chemical reaction activated by high-energy rays involves theradiolysis of water by the rays to produce a large number of reactivespecies. The reactive species are then reacted with a target substrate.In the products of water radiolysis, the compounds with the highestyields are hydroxyl radicals and hydrated electrons.

A living body is generally a reducing environment, and a large number ofsubstances such as glutathione and vitamin C can quench hydroxylradicals and increase the production of hydrated electrons. In thiscondition, using hydrated electrons to carry out chemical reactions willbe a big breakthrough in chemistry in vivo.

High-energy rays (such as X-rays and y-rays) can be used as externalstimuli to chemically react a complex having precursor ligands torelease functional molecules. Due to the high penetrating power of therays, as well as the high spatiotemporal resolution of the rays, theprecursor ligands can be activated very efficiently by radiotherapyapparatus. For example, X-ray irradiation as an external trigger foractivating precursor ligands can control radiation-induced chemicalreactions in space and time, and thus can precisely control the area,time and dose of such precursor ligands converted to their active forms.

The radiochemical change of molecules is the material basis for thestudy of all radiochemical effects. There are two main types ofradiochemical effects: direct effects in which ionizing radiation causesdirect chemical changes in target molecules, and indirect effects inwhich radiation deposits on environmental molecules and then causesindirect chemical interactions in target molecules. Direct and indirecteffects exist simultaneously, but indirect effect dominates in vivo.Because the tissue comprises 70-80% water, various active substances aremainly produced through the radiolysis of water (Scheme 1a), whereinsubstances with the highest yields are hydroxyl radicals (OH) andhydrated electrons (e_(aq) ⁻). The radiolysis of water is completedwithin 10⁻⁴ seconds, so the radiation-induced reaction tends to occurinstantaneously, and thus has strong controllability. OH-inducedcleavage chemistry reaction and related fluorescent probes have beensuccessfully used in bioimaging, but the rapid quenching of OH by thereducing tumor microenvironment hinders its development in livingsystems. However, the yield of radiation-induced e_(aq) ⁻, another majorproduct of water radiolysis, increases in reducing environments.Therefore, here we explore the feasibility of locally generating e_(aq)⁻ by precise radiotherapy to mediate chemical cleavage reactions (Scheme1b), and the use of radiation as a chemical tool to release targetmolecules in a highly tumor-selective manner (Scheme 1c).

Scheme 1. Radiation-induced controlled release of metal complexes intumors. a, Radiolysis of water by ionizing radiation. The G value ofhydrated electrons is 2.63 (G value refers to the number of moleculesformed by absorbing 100 eV energy in the system). b, Radiation-generatedhydrated electrons can reduce metal ions and metal complexes. c, Pt(IV)complexes can be reduced by irradiation and release Pt(II) anticancerdrugs and active axial ligands (such as fluorescent probes or anticancerdrugs).

In order to explore the reaction process, the solution ofoxaliPt(IV)-(Suc)₂ (80 mM, D₂O) was deoxygenated and then subjected toirradiation with 40 kGy of γ-rays (⁶⁰Co source, 200 Gy/min. 200 min,FIG. 5 a ). The irradiated solution was detected by UPLC-MS, and onlyone new peak was observed, wherein the retention time (FIG. 5 b ) andmass spectrometry signal (FIG. 5 c ) were both consistent with those ofthe oxaliplatin standard sample. The product was analyzed by nuclearmagnetic resonance (NMR). ¹⁹⁵Pt-NMR showed that the peak of the Pt(IV)complex at 1615 ppm almost disappeared after irradiation (FIG. 5 d top),and a new singlet peak appeared at −1988 ppm (FIG. 5 d middle), whichwas within the chemical shift range of the Pt(II) complex and coincidedwith that of oxaliplatin (FIG. 5 d bottom). The above tests all provedthat the release of axial ligands was caused by radiation reduction ofPt(IV) rather than hydrolysis.

To explore the generalizability of this strategy, we further conductedthe same study on two other platinum-based drugs commonly used globally,carboplatin and cisplatin. NMR characterization revealed thatcisPt(IV)-(Suc)₂ and carboPt(IV)-(Suc)₂ would release the correspondingPt(II) drugs after γ-ray irradiation in D₂O (FIG. 5 e, f ). In view ofthe wide application of platinum-based drugs in chemotherapy; thestrategy proposed in this work to control the release of Pt(II) byreduction of Pt(IV) prodrugs driven by radiation is very promising inrealizing precision chemotherapy driven by radiotherapy.

FIG. 5 exemplifies the broad-spectrum and high-efficiency release ofFDA-approved Pt(II) drugs from Pt(IV) complexes driven by radiation. a,Schematic illustration of release of Pt(II) drugs from Pt(IV) complexesdriven by radiation. b, UPLC chromatograms of oxaliPt(IV)-(Suc)₂,oxaliPt(IV)-(Suc)₂+radiation, oxaliplatin, and oxaliPt(IV)-(OH)₂, whereoxaliplatin and oxaliPt(IV)-(OH)₂ were used as a reference. The mainproduct released from oxaliPt(IV)-(Suc), driven by radiation had thesame retention time as that of oxaliplatin. The detector wavelength wasset at 254 nm. c, MS of the product released from oxaliPt(IV)-(Suc)₂driven by radiation showed that the released product was oxaliplatin.d-f, Study of Pt(II) drugs released from Pt(IV) complexes by nuclearmagnetic resonance (NMR). d, ¹⁹⁵Pt-NMR spectra of oxaliPt(IV)-(Suc)₂(1615 ppm, top), radiation product (−1988 ppm, middle) and externalstandard (bottom). e, ¹⁹⁵Pt-NMR spectra of cisPt(IV)-(Suc)₂ (1082 ppmtop), radiation product (−2150 ppm, middle) and external standard(bottom). f, ¹⁹⁵Pt-NMR spectra of carboPt(IV)-(Suc)₂ (1883 ppm, top),irradiation product (1707 ppm, middle) and external standard (bottom).¹⁹⁵Pt-NMR spectrum showed that the release of FDA-approved Pt(II) drugsdriven by radiation is effective and generally applicable to Pt(IV)complexes.

The present disclosure provides a metal complex of general formula (I),

L_(x)-M-P  (I)

wherein M is tetravalent platinum; L is independently for eachoccurrence a neutral ligand or anionic ligand; x is an integer from 1 to5; and P is a precursor ligand, the precursor ligand being a ligand of atetravalent platinum ion which can be released from the complex andconverted into a functional molecule D after irradiation.

L can be an axial ligand and/or a lateral ligand in the tetravalentplatinum complex. Ligand L is a ligand capable of being coordinated withtetravalent platinum or divalent platinum. In a preferred embodiment,the ligand L is a ligand capable of being coordinated with tetravalentplatinum or divalent platinum to form a stable complex. In a morepreferred embodiment, the ligand L, which is a lateral ligand, stillkeeps stable complexes with platinum ions after irradiation.

The choice of x is such that all L and P meet the requirement of a totalof six coordinations. When x is 2-5, those L in the complex can be thesame or different. In some embodiments, both L and P are ligands havingone coordination, and x is 5. In some embodiments, L is a ligand havingone coordination, P is a ligand having two coordinations, and x is 4.

In some embodiments, the functional molecule D includes but is notlimited to drug molecules, fluorescent molecules, or functional materialmolecules. The tetravalent platinum ion complex of the presentdisclosure is unique in that at least one axial ligand is released fromthe complex to form a functional molecule after irradiation. In oneembodiment, both axial ligands are released from the complex afterirradiation.

In some embodiments, the functional molecule D is an anticancer drugmolecule. In some preferred embodiments, the functional molecule D is ananticancer drug molecule, and at least one L has a group targeting tumorcells. For example, the L having a group targeting tumor cells includesa sugar transporter targeting group, a glutamine receptor targetinggroup, a phosphate receptor targeting group, an epidermal growth factorreceptor targeting group, an integrin targeting group, an energymetabolism enzyme targeting group, a chondriosome targeting group, aserum albumin targeting group, an inflammatory factor targeting group, aDNA targeting group, a histone deacetylase (HDAC) targeting group, a P53gene activator group, a tubulin inhibitor group, a cyclin-dependentkinase inhibitor group, or an indoleamine 2,3-dioxygenase inhibitorgroup.

In some embodiments, the functional molecule D is selected frommonomethyl auristatin E, monomethyl auristatin F, ibrutinib, acatinib,zanubrutinib, doxorubicin, mitomycin-C, mitomycin-A, daunorubicin,aminopterin, actinomycin, bleomycin, 9-aminocamptothecin,N8-acetylspermidine, 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine,yunnanmycin, gemcitabine, cytarabine, dolastatin, dacarbazine,5-fluorouracil, paclitaxel, docetaxel, gemcitabine, cytarabine, and6-mercaptopurine. In some preferred embodiments, the functional moleculeD is monomethyl auristatin E, monomethyl auristatin F, or5-fluorouracil.

In some embodiments, at least one ligand L is selected from the groupconsisting of: NH₃, ethylenediamine, F⁻, Cl⁻, oxalate, malonate,1,2-diaminocyclohexane, 1,2-diaminobenzene, 2-aminopropane,aminocyclohexane, cyclobutane-1,l-dicarboxylate, glycolate, lactate,aminocyclohexane, 2-isopropyl-4,5-bis(aminomethyl)-1,3-dioxolane,5-(triphenylphosphonio)valerate, succinate,6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoate, porphyrin, acetate,and propionate.

In some embodiments, one ligand L is an axial ligand capable of beingreleased from the complex after irradiation and converted into afunctional molecule which may be the same as or different from thefunctional molecule D.

In some embodiments, P is an axial ligand.

In some embodiments, P is ⁻O—C(═O)—X—Y, wherein

-   -   X is —NH—, —NR—, —O—, or —S—, R is an optionally substituted        C₁₋₁₀ alkyl group, and HXY constitutes the functional molecule        D; or    -   X is —CH₂—, —CRH—, or —CR₂—, wherein R is independently for each        occurrence an optionally substituted C₁₋₁₀ alkyl group, or two R        groups are taken together with the carbon atom to which they are        attached to form a 5-membered ring or a 6-membered ring, and        HOOCXY constitutes the functional molecule D.

In one embodiment, the optionally substituted C₁₋₁₀ alkyl is C₁₋₁₀ alkylor C₁₋₁₀ alkyl substituted by one or more substituents including, butnot limited to, halogen, —R₁, —NR₁R₂, —CN, —NO₂, —N₃, —OR₁, —SR₁,—NHCOR₁, —O—COR₁, —CH═CR₁R₂, —C(═O)—R₁, —C(═O)—OR₁, —C(═O)—Cl,—C(═O)—NH₂, —C(═O)—NH—R₁ and —C(═O)—NR₁R₂, wherein R₁ and R₂ areindependently selected from H, C₁-C₆ alkyl, C₁-C₆ haloalkyl, C₂-C₆alkenyl, C₃-C₁₀ cycloalkyl, C₆-C₂₀ aryl or heteroaryl with 5-20 ringatoms, wherein the alkyl, alkenyl, cycloalkyl, aryl and heteroaryldescribed for the substituent are optionally substituted by one or moreof halogen, hydroxyl, mercapto, —NH₂, —CN, —NO₂, —N₃, —NHCOH, —OC(═O)H,—C(═O)H, —C(═O)—OH, —C(═O)—Cl, —C(═O)—NH₂, —C(═O)—NH—CH₃, —C(═O)—CH₃,—C(═O)—OCH₃, C₁-C₆ alkyl, C₁-C₆ alkoxy, C₁-C₆ haloalkyl, C₂-C₆ alkenyl,C₃-C₁₀ cycloalkyl, C₆-C₂₀ aryl, or heteroaryl with 5-20 ring atoms.

Another aspect of the present disclosure also provides a use of theabove metal complex of general formula (I) in the fields of medicine,detection or functional materials, etc., wherein the metal complex ofgeneral formula (I) releases a functional molecule from a ligand afterirradiation to realize functions such as medicine, fluorescencedetection, or functional materials.

In some embodiments, on the one hand, the tetravalent platinum complexof the present disclosure is used as a precursor of a divalent platinumdrug, and is reduced by hydrated electrons generated by irradiation toobtain a divalent platinum product having pharmaceutical activity suchas anticancer activity; on the other hand, one or two axial ligandmolecules in the tetravalent platinum complex undergo a chemicalreaction by irradiation to release one or two functional molecules,which synergistically exert drug activity with the divalent platinumproduct, thereby reducing the effective dosage of the tetravalentplatinum complex, and thus reducing the toxic and side effects of thedrug.

In some embodiments, the tetravalent platinum complex of the presentdisclosure can introduce a targeting group into axial ligands or lateralligands, thereby improving the targeting of the platinum compound. Forexample, groups such as a sugar transporter targeting group, a glutaminereceptor targeting group, a phosphate receptor targeting group, anepidermal growth factor receptor targeting group, an integrin targetinggroup, an energy metabolism enzyme targeting group, a chondriosometargeting group, a serum albumin targeting group, an inflammatory factortargeting group, a DNA targeting group, a histone deacetylase (HDAC)targeting group, a P53 gene activator group, a tubulin inhibitor group,a cyclin-dependent kinase inhibitor group, or an indoleamine2,3-dioxygenase inhibitor group can be introduced into axial ligands orlateral ligands of the tetravalent platinum complex to improvetargeting. For details, please refer to “Chemistry Progress”, 201830(6), pages 831-846, the entire content of which is incorporated hereinas a part of the present disclosure.

In one embodiment, an antibody molecule or polypeptide is introducedinto the lateral or axial ligands of tetravalent platinum. For theintroduction of antibody molecules or polypeptides into ligands, pleaserefer to, for example, Green Chem., 2020, 22, 2203-2212.

In one embodiment, Herceptin is incorporated into the axial or lateralligands of the tetravalent platinum complex. In a preferred embodiment,Herceptin is incorporated into the axial ligand of the tetravalentplatinum complex.

In one embodiment, a targeting ligand may comprise a maleimide group,wherein the maleimide group is attached to an antibody or polypeptidevia sulfhydryl group.

In one embodiment, a targeting ligand may comprise a succinimide group,wherein the succinimide group is attached to an antibody or polypeptidevia amino group.

In one embodiment, a targeting ligand can be a targeting polypeptidemolecule, such as prostate-specific membrane antigen (PSMA), arginine(R)-glycine (G) aspartic acid (D) tripeptide, and chemokine receptor(CXCR4), etc.

In one embodiment, a targeting ligand is a lateral ligand or an axialligand. In a preferred embodiment, the targeting ligand is an axialligand.

In some embodiments, the metal complex of general formula (I) is atetravalent platinum complex as shown below,

wherein H—OC(O)—X—Y or H—X—Y is a functional molecule.

Axial ligand L₅ is also a leaving group, which can be divided into threecategories:

-   -   1. a non-functional capping agent, such as acetic acid and other        molecules that do not have therapeutic or targeting effects;    -   2. a targeting molecule, which can be maleimide-containing        molecules for linking with antibody or polypeptide via        sulfhydryl groups; or succinimide-containing molecules for        linking with antibody or polypeptide via amino groups; or        directly linked polypeptide molecules with targeting effect,        such as PSMA, RGD, CXCR4, etc.;    -   3. a therapeutic molecule that is the same as another axial        ligand, or different from another axial ligand, wherein two        drugs may play a synergism role.

In one embodiment, the ligand P in the complex is obtained by thereaction shown below.

Hydroxylated tetravalent platinum and an equivalent molar amount ofactive ester are stirred in dimethyl sulfoxide at ambient temperature,such as room temperature, for example for 24 hours, to obtain the targetproduct. The solvent is lyophilized: and then the solid is washed withorganic solvents such as diethyl ether and ethanol in sequence to obtainthe purified target product. Active esters are either commerciallyavailable or prepared by conventional synthetic methods of organicchemistry. Active esters can be produced, for example, by the followingmethod.

wherein X is NH, NR, O or S.

Y—XH is dissolved in dichloromethane. An equivalent molar amount ofdisuccinimidyl carbonate is added, followed by an equivalent molaramount of diisopropylethylamine (DIPEA). The mixture is reacted for 12hours, and then purified by silica gel column to obtain the activeester.

wherein X is CH₂, CRH or CR₂.

A carboxylic acid Y X—COOH is dissolved in dichloromethane. Twoequivalents of diisopropylethylamine are added. One equivalent ofcondensing agent 1-ethyl-(3-dimethylaminopropyl)carbodiimidehydrochloride (EDCI), and then N-hydroxysuccinimide is added. Themixture is reacted for 12 hours, and then purified by silica gel columnto obtain the active ester.

In one embodiment, the present disclosure uses a primary or secondaryamine-containing drug as a functional molecule. In a preferredembodiment, an anticancer drug containing a primary or secondary amineis used as a functional molecule. Drugs containing a primary orsecondary amine include, for example, ibrutinib, acatinib, zanubrutinib,doxorubicin, mitomycin-C, mitomycin-A, daunorubicin, aminopterin,actinomycin, bleomycin, 9-aminocamptothecin, N8-acetylspermidine,1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine, yunnanmycin,gemcitabine, cytarabine, dolastatin, dacarbazine, 5-fluorouracil, andtheir derivatives. Drugs containing a primary or secondary amine alsoinclude amino derivatives of drugs that do not naturally contain aminogroups. In other words, drugs that do not originally contain aminogroups can be chemically modified to have amino groups, and then activeesters are prepared through primary or secondary amines and furtherreacted with hydroxylated tetravalent platinum to obtain tetravalentplatinum coordinated with ⁻O(O)C—X—Y ligand.

In a preferred embodiment, the functional molecule is monomethylauristatin E.

In one embodiment, the present disclosure uses a hydroxyl-containingdrug as a functional molecule. In a preferred embodiment, ahydroxyl-containing anticancer drug is used as a functional molecule.Hydroxyl-containing functional molecules include, for example,paclitaxel, docetaxel, gemcitabine, cytarabine, and the like.Hydroxyl-containing functional molecules also include hydroxyderivatives of drugs that do not naturally contain hydroxyl groups. Inother words, a drug that does not contain a hydroxyl group can bechemically modified to have a hydroxyl group, and then an active esteris prepared through the hydroxyl group and further reacted withhydroxylated tetravalent platinum to obtain tetravalent platinumcoordinated with ⁻O(O)C—X—Y ligand.

In one embodiment, the present disclosure uses a sulfhydryl-containingdrug as a functional molecule. In a preferred embodiment, asulfhydryl-containing anticancer drug is used as a functional molecule.The functional molecules containing a sulfhydryl group include, forexample, 6-mercaptopurine and the like. The sulfhydryl-containingfunctional molecules also include sulfhydryl derivatives of drugs thatdo not naturally contain sulfhydryl groups. In other words, drugs thatdo not originally contain sulfhydryl groups can be chemically modifiedto have a sulfhydryl group, and then active esters can be preparedthrough sulfhydryl groups and further reacted with hydroxylatedtetravalent platinum to obtain tetravalent platinum coordinated with⁻O(O)C—X—Y ligand.

Similar to drug molecules, active esters can also be prepared by otherfunctional molecules, and further be reacted with hydroxylatedtetravalent platinum to obtain tetravalent platinum coordinated with⁻O(O)C—X—Y ligand.

EXAMPLE

The starting materials for the examples are commercially availableand/or can be prepared in a variety of ways well known to those skilledin the art of organic synthesis. Those skilled in the art of organicsynthesis will appropriately select reaction conditions (includingsolvent, reaction atmosphere, reaction temperature, duration ofexperiment, and workup) in the synthetic methods described below. Thoseskilled in the art of organic synthesis will understand that thefunctional groups present on each part of the molecule should becompatible with the proposed reagents and reactions. NMR was recordedusing a Bruker AVANCE 400 MHz spectrometer. High-resolution mass spectrawere measured using a Bruker Fourier Transform Ion Cyclotron resonancemass spectrometer. The liquid chromatography-mass spectrometry used wasa Waters e2695 instrument equipped with a Waters 2995 PDA and a WatersAcquity QDA mass spectrometer.

The change of the valence state of metal ions will involve the transferof electrons. First, a large number of metal ions and metal complexeshave been studied on chemical reactions driven by high-energy rays.

The following metal salts and metal complexes were screened:

Operation steps of test: the compound was dissolved in ultrapure waterto prepare a 100 μM metal compound solution, and oxygen gas in thesolution was removed by bubbling nitrogen gas for 15 minutes. Thedeoxidized metal solution was irradiated with X-rays from radiotherapyapparatus (RAD⋅SOURCE, model RS 2000-225, irradiation parameter: 4Gy/min) to receive X-rays at a dose of 0-1000 Gy. Finally, the remainingamount of raw material was measured, the disappeared concentration ofthe reactant was calculated, and the radiation yield was calculated(radiation yield=disappeared concentration of reactant/radiation dose).

TABLE 1 Yield of reduced metal compounds under irradiation Sample codeand sample name Yield (nM/Gy)  1 (sodium chloride) (No metal cationreduction reaction occured)  2 (potassium chloride) (No metal cationreduction reaction occured)  3 (dipotassium hydrogen phosphate) (Nometal cation reduction reaction occured)  4 (magnesium chloride) (Nometal cation reduction reaction occured)  5 (ferric chloride) 578  6 566 7 572  8 (potassium permanganate) 64  9 (potassium dichromate) 87 10(nickel chloride) 347 11 655 12 478 13 (copper sulfate) 209 14 (silvernitrate) 576 15 (vitamin B12) 553 16 (iron porphyrin) 598 17 575 18 427

Summarizing the above results, it was found that compounds with two ormore stable valence states in aqueous solution can be reduced. At thesame time, it was found in tests that for metal complexes, accompaniedby the reduction of metal ions, the complexes usually had structuralchanges, and even released ligand compounds.

Molecular Synthesis Route:

Molecules 1-17 were all commercially available compounds.

General synthetic route for molecules 19-28:

Dihydroxylated tetravalent platinum was obtained by reactingcommercially available divalent platinum (1 mmol) with 3 mL of hydrogenperoxide for 3 hours, and then filtering. The target compound wasobtained by reacting tetravalent platinum with the active ester oftriphenylphosphonium (2.2 mmol).

Compound 19 detected by mass spectrometry: 511.62 (with two positivecharges)

Compound 20 detected by mass spectrometry: 547.66 (with two positivecharges)

Compound 21 detected by mass spectrometry: 560.67 (with two positivecharges)

Compound 22 detected by mass spectrometry: 513.65 (with two positivecharges)

Compound 23 detected by mass spectrometry: 560.69 (with two positivecharges)

Compound 24 detected by mass spectrometry: 597.69 (with two positivecharges)

Compound 25 detected by mass spectrometry: 551.65 (with two positivecharges)

Compound 26 detected by mass spectrometry: 553.67 (with two positivecharges)

Compound 27 detected by mass spectrometry: 553.16 (with two positivecharges)

Compound 28 detected by mass spectrometry: 511.62 (with two positivecharges)

General Synthetic Route for Molecules 29-31:

The target products 29-31 were obtained by reacting hydroxylatedtetravalent platinum with an equivalent molar amount of active ester andthen adding two equivalents of succinic anhydride.

Compound 29 detected by mass spectrometry: 675.06 (with one negativecharge)

Compound 30 detected by mass spectrometry: 747.16 (with one negativecharge)

Compound 31 detected by mass spectrometry: 773.17 (with one negativecharge)

General Synthetic Route for Molecules 32-34:

The target products 32-34 were obtained by reacting hydroxylatedtetravalent platinum with an equivalent molar amount of active carbamateand then adding two equivalents of succinic anhydride.

Compound 32 detected by mass spectrometry: 633.01 (with one negativecharge)

Compound 33 detected by mass spectrometry: 705.10 (with one negativecharge)

Compound 34 detected by mass spectrometry: 731.11 (with one negativecharge)

Synthetic Steps of Molecule 35

Tetravalent platinum was obtained by oxidizing oxaliplatin, and thenreacted with an equivalent molar amount of active ester, and furtherreacted with an equivalent molar amount of active carbamate to obtainproduct 35.

Molecule 35 detected by mass spectrometry: 1047.35 (with one positivecharge)

Synthesis of Molecules 36-38

Dihydroxylated tetravalent platinum was obtained by reactingcommercially available oxaliplatin (10 mmol) with 30 mL of hydrogenperoxide for 3 hours and then filtering.

Compound 37 was obtained by reacting tetravalent platinum with an activeester of maleimide (12 mmol) in 10 mL of DMF for 12 hours, and thenpurified by silica gel column chromatography with DCM:MeOH=9:1 as aneluent.

Compound 38 was obtained by dissolving compound 37 in DMF, addingsuccinimidyl carbonate (24 mmol), and reacting for 6 hours, and thenpurified by silica gel column chromatography with DCM:MeOH=20:1 as aneluent.

Compound 36 was obtained by dissolving compound 38 in DMF, adding MMAE(10 mmol), and reacting for 24 hours, and then purified by silica gelcolumn chromatography with DCM:MeOH=20:1 as an eluent.

Molecule 37 detected by mass spectrometry: 625.14 (positive ion peakwith one hydrogen added)

Molecule 38 detected by mass spectrometry: 766.15 (positive ion peakwith one hydrogen added)

Molecule 36 detected by mass spectrometry: 1368.62 (positive ion peakwith one hydrogen added)

We performed studies with platinum-based complexes to determine thefeasibility of this radiation-activation approach in vivo. Firstly, thetetravalent platinum complex was irradiated with high-energy rays toprove that the reaction has a broad spectrum for platinum-based drugs,and the results are shown in FIG. 1 .

Operation steps of test: the tetravalent platinum complex was dissolvedin ultrapure water to prepare a 10 μM solution, and at the same timeoxygen gas in the solution was removed by bubbling nitrogen gas. Thedeoxygenated tetravalent platinum complex solution was irradiated byX-rays from radiotherapy apparatus (RAD⋅SOURCE, model RS 2000-225,irradiation parameter: 4 Gy/min) to receive X-rays at a dose of 0-60 Gy.The peak area of the newly generated axial ligand peak was detected byultra-high performance liquid chromatography, and the release of axialligand during irradiation was determined by the standard curve of thepeak area-concentration plot of the pure ligand in HPLC.

The test results of the ligand release ratio (actual release of axialligand after reaction to theoretically complete release of axial ligand)of 10 μM tetravalent platinum complexes 19-31 after 60 Gy of X-rayirradiation were shown in FIG. 1 . After the detection of radiationactivation of molecules 19 to 31, it was confirmed that the reduction oftetravalent platinum metal complexes by high-energy rays and the releaseof axial ligands have broad spectrum.

To apply this radiation-activated chemical reaction in vivo, a problemmust be solved, i.e., the complex needs to keep stable in the reducingenvironment in vivo. Platinum drugs that have been approved by the FDAinclude cisplatin, carboplatin and oxaliplatin. In the tetravalentplatinum precursors that use these three platinum drugs as the parent,is there any tetravalent platinum drug that is stable in the reducingenvironment in vivo, especially in tumors? At the same time, does thismethod only release carboxyl ligands? Compounds 32, 33 and 34 were usedfor stability screening because there were a large number of drugscontaining amino groups. The result was shown in FIG. 2 .

Steps of test: Compounds 32, 33, and 34 were respectively dissolved inpure water to prepare a 10 μM solution, and at the same time, nitrogengas was bubbled to remove oxygen gas in the solution. The deoxygenatedtetravalent platinum complex solution was irradiated by X-rays fromradiotherapy apparatus (RAD⋅SOURCE, model RS 2000-225, irradiationparameter: 4 Gy/min) to receive X-rays at a dose of 0-60 Gy. The releaseof axial ligands was detected by ultra-high performance liquidchromatography. The results of the compound's response to high-energyradiation were thus obtained.

32, 33, and 34 were dissolved respectively in pure water to prepare a 10μM solution, and at the same time oxygen gas in the solution wasremoved. Endogenous reducing substance vitamin C was then added, so thatthe concentration of vitamin C was 2 mM. The co-incubation time was 24h, and the release of axial ligands in different time periods wasdetected. The stability of the compounds under reducing environments wasthus determined.

A tetravalent platinum complex with oxaliplatin as the parent wasformulated to obtain a 10 μM solution, and oxygen gas was removed fromthe solution. Various types of endogenous reducing substances (cysteine,glutathione, reduced nicotinamide adenine dinucleotide phosphate) werethen added at different concentrations. In this way, the stability ofthe compounds against endogenous reducing substances in the cellularenvironment or in vivo environment was determined.

FIG. 2 is the test results of screening tetravalent platinum compounds32, 33 and 34 on stability in vivo. In FIG. 2 , (A) shows the structuresof the three platinum compounds used in the study; (B), (G), and (I) arethe reaction schematic diagrams of the three tetravalent platinumcompounds: (C) is the fluorescence change diagram of molecule 34 afterco-incubation with Vc, and it can be seen that molecule 34 wasrelatively stable in the presence of Vc, and no reduction reactionoccurred; (D) is the fluorescence change diagram of molecule 34 afterbeing irradiated, and it can be seen that the relative fluorescenceintensity is linearly correlated with the irradiation dose: (E) is theUPLC change diagram after co-incubation of molecule 34 and Vc, and itcan be seen that no new coumarin peak was generated after co-incubationof molecule 34 and Vc; (F) is the UPLC change diagram of molecule 34after receiving irradiation, and it can be seen that during theirradiation, the axial ligand coumarin was gradually released with theincrease of irradiation dose; (H) is the fluorescence change diagram ofmolecule 32 after co-incubation with Vc; (J) is the fluorescence changediagram of molecule 33 after co-incubation with Vc.

After confirming that the compound with oxaliplatin as the parent wasstable and can be activated by high-energy rays in a test tube, thefeasibility of this activation method in vivo was studied. Molecule 35was designed so that ligand released upon activation can emit thenear-infrared fluorescence, and the axial ligand release in vivo can benondestructively determined. The test result is shown in FIG. 3 .

Test Steps:

Test in test tube: molecule 35 was dissolved in pure water to prepare a10 μM solution, and at the same time oxygen gas in the solution wasremoved. The deoxygenated tetravalent platinum complex solution wasirradiated by X-rays from radiotherapy apparatus (RAD⋅SOURCE, model RS2000-225, irradiation parameter: 4 Gy/min) to receive X-rays at a doseof 0-60 Gy. Change in the fluorescence signal of the solution was thendetected with a small animal imager.

Cell test: molecule 35 was dissolved in HBSS buffer to prepare a 10 μMsolution, and at the same time oxygen gas in the solution was removed.Then the solution was incubated with the cells, and then the mixture wasirradiated with X-rays from the radiotherapy apparatus to receive X-raysat a dose of 0-16 Gy. The fluorescent signal of the cells was detectedwith a confocal microscope.

In vivo test: molecule 35 was dissolved in DMSO to prepare a 20 mM stocksolution. 20 μL of phosphate buffer solution (pH=7.4) containing 1% DMSO(in which the concentration of 35 was 200 μM) was injected into thetumor area of mice. Tumors were then irradiated locally with X-rays atdoses of 0, 4, and 12 Gy, respectively. The fluorescence signal of thetumor area was then detected with a small animal imager.

FIG. 3 shows an in vivo activation test of tetravalent platinum withoxaliplatin as the parent. In FIG. 3 , (A) is schematic diagram of thestructure and activation of molecule 35: (B) is schematic diagram of therelease of axial ligands by molecule 35 in a test tube; (C) is aconfocal image of molecule 35 activated in a cell environment; (D) is asmall animal imaging image of molecule 35 activated in a mouse tumormodel.

Test results showed that molecule 35 can be reduced to release ligandsby high-energy rays in test tubes, cells and mouse models in vivo, andthis release strategy has been proved in concept.

Activation of chemotherapeutics by radiotherapy is in line with the goalof precision medicine, which can be achieved with antibody-drugconjugates. The prodrug compound 36 was prepared by using theoxaliplatin parent as a linker, and the antibody-drug conjugate wasprepared by linking 36 with the antibody Herceptin. The antibody-drugconjugate was studied in a mouse treatment test, and the result wasshown in FIG. 4 .

Test Steps

Preparation of antibody-drug conjugate (ADC): 200 μL of phosphatebuffered saline solution was added to a 1.5 mL centrifuge tube, then 100μL of 50 mg/mL Herceptin solution was added. Afterwards, 75 μL of 1 mMTECP was added and reacted for 1.5 h for opening disulfide bond. Then,35 μL of 10 mM compound 36 in DMSO was added to the reaction solution,and reacted for 1 h. Unreacted small molecules were removed byultrafiltration centrifugation to obtain antibody-drug conjugate.

Antibody-drug conjugate release test in vitro: the preparedantibody-drug conjugate was diluted to 50 nM, and irradiated with 0-16Gy of X-ray (RAD⋅SOURCE, model RS 2000-225, irradiation parameter: 4Gy/min). The mass spectrum signal intensity of the functional moleculeMMAE was detected by mass spectrum. The release amount of MMAE wasdetermined through the external standard curve, that is, the MMAEconcentration-mass spectrum signal intensity curve.

Cytotoxicity test: different concentrations of antibody-drug conjugateswere incubated with cells and irradiated with different doses of X-raysto determine the half-inhibitory concentration of antibody-drugconjugates on cancer cells under different conditions.

Animal treatment test: the mice were divided into four groups, whereinthe first group was only injected with PBS solution, the second groupwas injected with PBS and then irradiated with X-ray, the third groupwas only injected with platinum antibody-drug conjugate, and the fourthgroup was injected with the antibody-drug conjugate and then irradiatedwith X-ray. Tumor volume was measured.

FIG. 4 is a radiation-responsive antibody-drug conjugate with platinumas a linker. In FIG. 4 , (A) shows schematic diagram of the activationof antibody-drug conjugate (ADC) to release MMAE; (B) shows release testof antibody-drug conjugate (50 nM) in a test tube; (C) showscytotoxicity test of antibody-drug conjugate; (D) shows body weightchange curve of mice; (E) shows mice tumor growth curve; (F) shows tumorimage on day 24; (G) shows tumor mass image on day 24.

This treatment method can significantly inhibit the growth of tumors,and has extremely high clinical application value.

The examples of the present disclosure demonstrate in principle thefeasibility of a strategy of irradiating tetravalent platinum complexesto release functional molecules. Further, the examples of the presentdisclosure use a MMAE functional molecule as a model to illustrate thefeasibility of the strategy of irradiating tetravalent platinumcomplexes to release drug molecules. The examples of the presentdisclosure also demonstrate that the concentration of a functionalmolecule released from a complex has a good linear relationship with adose.

A prodrug is an inactive substance that is converted into an active drugin the body by the action of enzymes or other chemicals. This approachis widely used in the pharmaceutical industry and requires the releaseof sufficiently high concentrations of the drug at the desired location.Antibody-drug conjugate (ADC) is a perfect example, where its tumorselectivity makes it promising, but is often hampered bydifficult-to-control drug release. In fact, classical ADC (such asTDM-1) requires receptor-mediated endocytosis for drug release, and thetherapeutic effect on heterogeneous tumors is not satisfactory. Toimprove therapeutic efficacy and reduce side effects, scientists havedeveloped many drug release strategies. In clinical research, ADClinkers are often non-cleavable, or require endogenous stimuli such asacidic conditions, lysosomal proteases, and GSH to initiate cleavage.Few release strategies mediated by exogenous stimuli (such as smallchemical molecules) have entered clinical research, mainly because sideeffects caused by small chemical molecules are difficult to be assessedin clinical trials. Therefore, we attempted to investigate whetherradiation-driven cleavage chemistry could be applied to the release ofADC-loaded drugs to improve the release efficiency of drugs in tumors.Firstly, using an oxaliPt(IV)-OH carbamate linker, monomethyl auristatinE (MMAE) was linked to monoclonal anti-HER2 antibody trastuzumab, acommonly used ADC system (FIG. 6 a ). The OxaliPt(IV)-carbamate linkerresponds selectively to X-ray-generated a and further decarboxylates torelease an axial ligand, giving highly toxic free MMAE (FIG. 6 a ).

Following the established method, 2.2 equivalents of TECP were used toreduce trastuzumab to free thiols without reducing the oxaliPt(IV)complex, and then 10 equivalents of MMAE were directly added to thereaction. The crude product was purified by PD-10 column. Highperformance liquid chromatography (HPLC) showed that thetrastuzumab-oxaliPt(IV)-MMAE (oxaliPt(IV)-ADC) conjugate had a main peak(FIG. 6 b ): MALDI-TOF-MS analysis showed that the main peak of eachantibody contained 4 payloads (FIG. 6 c ), which was the optimaldrug-to-antibody ratio (DAR) for tumor-selective drug delivery in vivo.

To test whether radiation-driven release would achieve drug release fromADCs, we chosed to use BGC823 cells, a human gastric cancer cell linewith moderate levels of HER2 expression, for cell viability tests ofoxaliPt(IV)-ADC+X-rays (FIG. 6 d ). BGC823 cells were treated with onlyoxaliPt(IV)-ADC under hypoxic conditions, with only oxaliPt(IV)-ADCunder normoxia conditions, and with oxaliPt(IV)-ADC+8 Gy X-rays undernormoxia conditions. After 96 hours of culture, CCK8 detection showedthat the cell viability in the oxaliPt(IV)-ADC+8 Gy X-rays treatmentgroup was significantly decreased, with IC50 of 2.60±1.60 nM. Incontrast, the IC50 of oxaliPt(N)-ADC was 85.90±24.16 nM. Therefore,radiation-driven oxaliPt(IV)-ADC was 33 times more cytotoxic thanoxaliPt(IV)-ADC in a BGC823 cell line. Under hypoxic conditions,oxaliPt(IV)-ADC showed no observable cytotoxicity, indicating good invitro stability of oxaliPt(N)-ADC.

FIG. 6 depicts the construction and characterization of ADCs whose drugrelease can be driven by radiotherapy: a, schematic diagram of thestructure of trastuzumab-Pt(IV)-MMAE conjugated drug (oxaliPt(IV)-ADC),and the X-ray-driven release of the drug MMAE thereof b, the purity ofoxaliPt(IV)-ADC determined by HIC-HPLC. c, MALDI-TOF analysis showedthat the drug-antibody ratio of oxaliPt(IV)-ADC was about 4. d, Cellsurvival rate of BGC823 cells treated with MMAE, oxaliPt(IV)-ADC,oxaliPt(IV)-ADC+8 Gy X-rays.

When using Positron Emission Tomography-Computed Tomography (PET-CT)imaging to study the pharmacokinetics of oxaliPt(IV)-ADC in BGC823tumor-bearing mice, firstly, oxaliPt(IV)-ADC was labeled with⁸⁹Zr—Zr(oxalate)₂. PET-CT imaging at multiple time points (FIG. 7 a )showed that ⁸⁹Zr-oxaliPt(IV)-ADC showed good blood circulation, andtumor uptake began 6 hours after administration, and gradually increasedwith time, until reaching equilibrium at 36 hours (10% ID/g, FIG. 7 b ).After 48 hours of administration, the radioactive uptake in the tumorwas significantly higher than that in the blood, and the drug content inthe blood continued to decrease, while the drug uptake of the tumorcontinued to increase (FIG. 7 b ). Studying the pharmacokinetics ofdrugs helps to understand the dynamic distribution of ADCs in mice anddetermine the correct time for tumor irradiation to obtain the optimaltime point of radiotherapy and chemotherapy. As shown in FIG. 7 d ,BGC823 tumor mice were randomly divided into 4 groups: control groups(non-cleavable ADC (NC-ADC), oxaliPt(IV)-ADC, NC-ADC+X-ray) andoxaliPt(IV)-ADC+X-ray treatment group. All mice were injected with 5mg/kg ADC on day 0. For the treatment group, 8 Gy of X-rays were givenon day 2 after ADC injection according to the previous in vivobiodistribution. The mice were then dissected, and xenogeneic tumorswere collected. The intratumoral concentration of MMAE was analyzed byLC-QTOF-MS. The results showed that the drug release of MMAE in thetreatment group was at least 3 times higher than that in the group usingoxaliPt(IV)-ADC alone. For NC-ADC, there was no difference in therelease of MMAE with or without X-rays, indicating that the release ofMMAE depends on the reduction of Pt(IV) by X-rays. It indicates thefeasibility of radiation-driven chemical cleavage reaction to releasedrugs and realize tumor therapy.

FIG. 7 depicts the pharmacokinetic study of OxaliPt(IV)-ADC: a, PET-CTimages of BGC823 tumor-bearing mice after intravenous injection of[⁸⁹Zr]oxaliPt(IV)-ADC. b, Time-activity curves (TAC) of[⁸⁹Zr]oxaliPt(IV)-ADC in blood, liver and tumor. c, MMAE concentrationsin tumors detected after mice were treated with oxaliPt(1V)-ADC (5mg/kg) or NC-ADC (5 mg/kg) alone, or with oxaliPt(IV)-ADC (5mg/kg)+X-rays (8 Gy), or with NC-ADC (5 mg/kg)+X-rays (8 Gy).

The above descriptions are only exemplary embodiments of the presentdisclosure, and are not intended to limit the protection scope of thepresent disclosure, which is determined by the appended claims.

This application claims the priority of the Chinese patent applicationNo. 202011337782.X filed on Nov. 25, 2020, and the content disclosed inthe above Chinese patent application is incorporated in its entirety asa part of this application.

1. A metal complex of general formula (I),L_(x)-M-P  (I) wherein: M is tetravalent platinum; L is independentlyfor each occurrence a neutral ligand or an anionic ligand; x is aninteger from 1 to 5; and P is a precursor ligand, the precursor ligandbeing a ligand of the tetravalent platinum ion which can be releasedfrom the complex after irradiation and converted into a functionalmolecule D.
 2. The metal complex according to claim 1, wherein thefunctional molecule D is selected from drug molecules, fluorescentmolecules, and functional material molecules.
 3. The metal complexaccording to claim 2, wherein the functional molecule D is an anticancerdrug molecule.
 4. The metal complex according to claim 3, wherein atleast one L has a group targeting tumor cells.
 5. The metal complexaccording to claim 4, wherein the L having a group targeting tumor cellsincludes a sugar transporter targeting group, a glutamine receptortargeting group, a phosphate receptor targeting group, an epidermalgrowth factor receptor targeting group, an integrin targeting group, anenergy metabolism enzyme targeting group, a chondriosome targetinggroup, a serum albumin targeting group, an inflammatory factor targetinggroup, a DNA targeting group, a histone deacetylase (HDAC) targetinggroup, a P53 gene activator group, a tubulin inhibitor group, acyclin-dependent kinase inhibitor group, or an indoleamine2,3-dioxygenase inhibitor group.
 6. The metal complex according to claim2, wherein the functional molecule D is selected from monomethylauristatin E, monomethyl auristatin F, ibrutinib, acatinib,zanubrutinib, doxorubicin, mitomycin-C, mitomycin-A, daunorubicin,aminopterin, actinomycin, bleomycin, 9-aminocamptothecin,N8-acetylspermidine, 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine,yunnanmycin, gemcitabine, cytarabine, dolastatin, dacarbazine,5-fluorouracil, paclitaxel, docetaxel, and 6-mercaptopurine.
 7. Themetal complex according to claim 6, wherein the functional molecule D ismonomethyl auristatin E, monomethyl auristatin F, or 5-fluorouracil. 8.The metal complex according to claim 1, wherein at least one ligand L isselected from: NH₃, ethylenediamine, F⁻, Cl⁻, oxalate, malonate,1,2-diaminocyclohexane, 1,2-diaminobenzene, 2-aminopropane,aminocyclohexane, cyclobutane-1,1-dicarboxylate, glycolate, lactate,aminocyclohexane, 2-isopropyl-4,5-bis(aminomethyl)-1,3-dioxolane,5-(triphenylphosphonio)valerate, succinate,6-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)hexanoate, porphyrin, acetate,and propionate.
 9. The metal complex according to claim 1, wherein oneligand L is an axial ligand capable of being released from the complexafter irradiation and converted into a functional molecule which may bethe same as or different from the functional molecule D.
 10. The metalcomplex according to claim 1, wherein P is an axial ligand.
 11. Themetal complex according to claim 1, wherein P is ⁻O—C(═O)—X—Y, wherein Xis —NH—, —NR—, —O—, or —S—, R is an optionally substituted C₁₋₁₀ alkyl,and HXY constitutes the functional molecule D; or X is —CH₂—, —CRH—, or—CR₂—, wherein R is independently for each occurrence an optionallysubstituted C₁₋₁₀ alkyl, or two R groups are taken together with thecarbon atom to which they are attached to form a 5-membered ring or a6-membered ring, and HOOCXY constitutes the functional molecule D. 12.The metal complex according to claim 1, wherein the metal complex ofgeneral formula (I) can release an axial ligand from the complex toobtain a divalent platinum complex after irradiation.
 13. The metalcomplex according to claim 12, wherein the divalent platinum complex hasan anticancer effect.
 14. A pharmaceutical composition comprising themetal complex according to claim
 1. 15. A method for treating a tumor,comprising: administering to a subject the metal complex according toclaim 1, and irradiating the subject.
 16. The method of claim 15,wherein the irradiation is from radiotherapy.
 17. A kit comprising: thepharmaceutical composition according to claim 14, and description,indicating that the administration is followed by radiation therapy totreat a tumor.
 18. A kit comprising: the metal complex according toclaim 1, and description, indicating that the administration is followedby radiation therapy to treat a tumor.